[sysctl(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl&section=8) is an interface that allows you to make changes to a running DragonFly system. This includes many advanced options of the TCP/IP stack and virtual memory system that can dramatically improve performance for an experienced system administrator. Over five hundred system variables can be read and set using [sysctl(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl&section=8).

If you want to set automatically some variables each time the machine boots, add them to the `/etc/sysctl.conf` file. For more information see the [sysctl.conf(5)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl.conf&section=5) manual page and the [configtuning-configfiles.html#CONFIGTUNING-SYSCTLCONF Section 6.10.4].

In some cases it may be desirable to modify read-only [sysctl(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl&section=8) values. While this is not recommended, it is also sometimes unavoidable.

Cases like the one above usually require the modification of some default [sysctl(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl&section=8) settings which are set read only. To overcome these situations a user can put [sysctl(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=sysctl&section=8) ***OIDs*** in their local `/boot/loader.conf`. Default settings are located in the `/boot/defaults/loader.conf` file.

Fixing the problem mentioned above would require a user to set `hw.pci.allow_unsupported_io_range=1` in the aforementioned file. Now [cardbus(4)](http://leaf.dragonflybsd.org/cgi/web-man?command=cardbus&section=4) will work properly.